Multi-layered interconnect modules are widely used in the semiconductor industry to mechanically support integrated circuit chips and electrically attach the chips to printed wiring boards. Interconnect modules can be configured to support a single chip or multiple chips, and are typically identified by the designation SCM (single chip module) or MCM (multi-chip module).
An interconnect module provides interconnections that serve to electrically couple an integrated circuit chip to signal lines, power lines, and other components carried by a printed wiring board. In particular, the interconnect module provides interconnections that redistribute the densely packed inputs and outputs (I/Os) of the chip to corresponding I/Os on the printed wiring board. In addition to electrical interconnection, an interconnect module typically serves to mechanically couple a chip to a printed wiring board, and may perform other functions such as heat dissipation and environmental protection.
To support high frequency operation, it is important to achieve a low impedance between the chip die and the power and ground distribution lines or planes within the module. For lower frequencies, sufficiently low impedance can be achieved by placing discrete decoupling capacitors within the package and on the printed wiring board. As frequencies increase, however, it becomes increasingly difficult to achieve adequately low impedance due to the inherent series inductance produced by the discrete capacitors. In addition, leads, solder bumps, vias, plated through holes, and traces in the interconnect module compound the inability of the discrete capacitors to function adequately at higher frequencies due to increased inductance.
As an alternative to discrete capacitors, some chips include internal capacitor structures formed within the die. Specifically, an “on-chip” capacitor can be fabricated during device manufacture, and provides low inductance paths between the capacitor, the power and ground lines, and the logic and buffer circuitry. Unfortunately, on-chip capacitors significantly increase the cost of integrated circuit chips by increasing die size and decreasing yield.
Moreover, the amount of on-chip capacitance that can be added to the die is typically limited by space constraints and the dielectric constant, which must be limited in order to avoid adversely affecting signal propagation characteristics of adjacent traces. Also, the interconnection between the on-chip capacitor and a driver or receiver is usually a relatively high resistance path due to the use of high resistivity metal, e.g., aluminum. Consequently, the utility of internal capacitors is limited.